1. Technical Field
The present disclosure relates to an organic light emitting diode display and manufacturing method thereof, and more particularly to an organic light emitting diode display having a stress buffer.
2. Discussion of Related Art
An organic light emitting diode (OLED) display is a self emissive display device, which displays images by exciting an emissive organic material to emit light. The OLED display includes an anode (i.e., hole injection electrode), a cathode (i.e., electron injection electrode), and an organic light emission layer interposed therebetween. When the holes and the electrons are injected into the light emission layer, they recombine to form excitons, which emit light when they change from an excited state to a ground state.
A plurality of pixels of the OLED display, each of the plurality of pixels including an anode, a cathode, and a light emission layer, are arranged in a matrix and driven in passive matrix (or simple matrix) addressing or active matrix addressing.
A passive matrix type OLED display includes a plurality of anode lines, a plurality of cathode lines intersecting the anode lines, and a plurality of pixels. Each of the plurality of pixels includes a light emission layer. In the passive matrix type OLED display, light emission of a pixel located at the intersection of selected signal lines occurs when one of the anode lines and one of the cathode lines are selected.
The active matrix type OLED display includes a plurality of pixels. Each of the plurality of pixels in the active matrix type OLED includes a switching transistor, a driving transistor, a storage capacitor, an anode, a cathode, and a light emission layer. The active matrix type OLED display further includes a plurality of gate lines transmitting gate signals and a plurality of data lines transmitting data voltages. The switching transistor is connected to one of the gate lines and one of the data lines, and transmits the data voltage from the data line in response to the gate signal. The driving transistor receives the data voltage from the switching transistor and drives a current having a magnitude determined based on the data voltage. The current from the driving transistor enters the light emission layer to cause light emission having an intensity based on the current. The storage capacitor is connected to the data voltage to maintain the data voltage. A gray scaling of the active matrix type OLED display is accomplished by controlling the data voltages to adjust the current driven by the driving transistor. The color representation of the OLED display is obtained by providing red, green and blue light emission layers.
The OLED display includes top emission type and bottom emission type based on a light emitting direction. The top emission type OLED display includes a transparent cathode made of, for example, indium tin oxide (ITO) or indium zinc oxide (IZO) and an opaque anode. The bottom emission type OLED display includes an opaque cathode and a transparent anode. Positions of the anode and the cathode can be altered.
The anode and cathode electrodes of an OLED display can be formed on an insulating layer that includes a flat surface for step coverage. The electrodes contacting the insulating layer can be cracked during a manufacturing process. The crack can also expand into the insulating layer, thereby reducing the productivity of OLED display.